Faraday Cup Plasma Instruments
Nithin Sivadas, 15 March 2021
In this talk, Dr. Justin Kasper engages us with a discussion on Faraday cups - a simple plasma instrument that can measure velocities, densities, temperature, and relative composition of plasma. It is a solid metal cup with conducting wire grids at different potentials to create regions with simple uniform electric fields. By varying the voltage applied to these wire grids, the instrument can allow particles of a specific energy range to pass into it, and output current is measured.
Dr. Kasper goes through the functional description and history of these instruments first and then proceeds into a discussion about the strengths and limitations of the Faraday cups. These devices are less sensitive to background radiation outside the measured energy range and are easy to calibrate. Their response is stable over long periods and does not vary with incident species. They have a substantial geometric factor and a large dynamic range. They can even estimate 3D velocity distribution functions if the spacecraft rotates or uses multiple detectors with different look-angles.
In the second half of the talk, Dr. Kasper discusses the Faraday Cup flown onboard the Solar Probe. Capable of withstanding high-temperature gradients ranging from 70 to 1800 degrees Celsius, the instrument has produced some stunning, high-resolution data. Dr. Kasper discusses the detector design, calibration, as well as the first data and its interpretation. Towards the end of the talk, Dr. Kasper mentions a couple of new missions flying Faraday cups and opens up the floor for some stimulating discussion.
You can find a recording of Dr. Kasper’s talk in our Youtube channel.